A “virtual machine” or a “VM” refers to a specific software-based implementation of a machine in a virtualization environment, in which the hardware resources of a real computer (e.g., CPU, memory, etc.) are virtualized or transformed into the underlying support for the fully functional virtual machine that can run its own operating system and applications on the underlying physical resources just like a real computer.
Virtualization works by inserting a thin layer of software directly on the computer hardware or on a host operating system. This layer of software contains a virtual machine monitor or “hypervisor” that allocates hardware resources dynamically and transparently. Multiple operating systems run concurrently on a single physical computer and share hardware resources with each other. By encapsulating an entire machine, including CPU, memory, operating system, and network devices, a virtual machine is completely compatible with most standard operating systems, applications, and device drivers. Most modern implementations allow several operating systems and applications to safely run at the same time on a single computer, with each having access to the resources it needs when it needs them.
Virtualization allows one to run multiple virtual machines on a single physical machine, with each virtual machine sharing the resources of that one physical computer across multiple environments. Different virtual machines can run different operating systems and multiple applications on the same physical computer.
One reason for the broad adoption of virtualization in modern business and computing environments is because of the resource utilization advantages provided by virtual machines. Without virtualization, if a physical machine is limited to a single dedicated operating system, then during periods of inactivity by the dedicated operating system the physical machine is not utilized to perform useful work. This is wasteful and inefficient if there are users on other physical machines which are currently waiting for computing resources. To address this problem, virtualization allows multiple VMs to share the underlying physical resources so that during periods of inactivity by one VM, other VMs can take advantage of the resource availability to process workloads. This can produce great efficiencies for the utilization of physical devices, and can result in reduced redundancies and better resource cost management.
In order to provide disaster recovery to or local/remote backups of VMs in a virtualization environment, snapshots of the VM state may be taken. These snapshots provide checkpoints of a VM's state at various points in time, and can be used to place a VM in a previous state for various disaster recovery or local/remote backup purposes. For example, a VM that has crashed may use a most recent snapshot to recover its state prior to crashing.
Snapshots may be taken of a VMs state at varying degrees of granularity. A crash-consistent snapshot includes the state of virtual resources for the VM, but may not include certain information regarding the state of the virtual operating system or applications running within the VM. Thus, a VM recovered from a crash-consistent snapshot may not exactly replicate its state prior to crashing. An application consistent snapshot includes the entire state of the VM, including the state of virtual resources, virtual operating system/kernel and applications running in the VM.
Conventionally, application specific snapshots for VMs are created by employing a third party backup server. The third party backup server manages the maintenance of VM snapshots by deploying a backup agent to run in the user-space of each of the VMs being managed. The backup agent at a given VM communicates with the hypervisor associated with the VM to create application consistent snapshots which are communicated to and maintained at the third party backup server. While the third party backup server is capable of properly maintaining application consistent backups of VMs, the need to create and deploy backup agents for different types of VMs becomes cumbersome. Because different VMs employ different operating systems/kernels, the third party backup server is required to create numerous different backup agent types in order to maintain snapshots for the various different VM types.
Therefore, there is a need for an improved approach for maintaining application consistent snapshots in a virtualization environment.